The term “capacity on demand” as it relates to computer systems refers generally to adding resources on an as-needed basis. In particular, processing capacity could be added on demand.
Known arrangements for adding processing capacity on demand involve providing latent processing capacity that is unused until a need for extra capacity arises. When a need arises, the latent processing capacity may be tapped, and then allowed to again become unused when the need passes. For example, latent processing capacity could be added to a high-end server in a data network such as the Internet, and called upon only during periods of peak traffic. Letting the processing capacity be unused until needed reduces costs, since agreements may be made with capacity providers that only capacity that is actually used will be paid for.
In some known arrangements, latent or reserve processing capacity may be provided in processor packages that are added to a system's hardware platform. The processor packages may be brought into use at a platform level, in a manner analogous to using a relay to connect power to a circuit to bring the circuit into use. When reserve capacity is used in this way, it involves adding the capacity in bulk form, that is, in units of one or more entire processor packages. Finer granularity is not possible, in that individual processing elements on a processor package cannot be selectively brought into use. Such an approach may be wasteful if all processing elements on a processor package are not needed.
Other known arrangements may be able to selectively activate individual processing elements on a processor package for added capacity. Such arrangements may use a form of power management to regulate how many processing elements are active. In this power management approach, processing elements not in use may be placed into a low power state to conserve energy, and then placed into a higher power state when put into use. Additionally, known power management techniques typically require that managed devices be made continuously “visible” (in an understood operating system software sense) to associated BIOS (Basic Input/Output System) and operating system software.